Species-level termite methane production rates

Termites consume substantial amounts of plant material across tropical and subtropical ecosystems. During the process of lignocellulose digestion, the symbiotic methanogenesis within termites’ guts produces the potent greenhouse gas methane (CH4). Termites contribute an estimated 1-5% of global CH4 emissions, with these estimates derived from the product of termite biomass and termite CH4 production rate per unit of termite biomass. However, termite CH4 production rates vary significantly across species, genus, family, and feeding group, yet our understanding of this variation remains poor. Here, we reviewed papers published from 1975 to 2021 to create a single consistently derived list of species-level termite CH4 production rates. We searched Google Scholar using two key words: termite AND methane. We only included studies that had measured termite CH4 production rates using the incubation method. For each eligible study, we extracted and tabulated termite CH4 production rates and other relevant variables (e.g., feeding groups). We used μg CH4 g-1(termite) h-1 as the standardized unit, and if other units were presented, we converted them into this standardized unit. Overall, These data include 134 termite species from 65 genera and 5 families. Termite CH4 production rates ranged from 0 to 25.26 μg CH4 g-1(termite) h-1, with an average rate of 3.74 (standard deviation = 4.08, n = 251). Reported CH4 production rates were largely concentrated in the family Termitidae. Across feeding groups, soil feeders tended to have higher CH4 production rates than wood feeders. However, published data represent fewer than 5% of described termite species, and therefore we hope that our study will initiate a community-wide effort to fill data gaps and advance our understanding of the role of termites in critical biogeochemical cycles and other ecosystem processes.

Methods
We collected termite CH4 production rates from the literature, including both peer-reviewed articles and book chapters. Data gathering was conducted in October 2020 and updated in February 2022. We searched Google Scholar using two key words: termite AND methane. All 7,699 search results were screened for eligibility. We only included studies that had measured termite CH4 production rates using the incubation method, which involves sealing a known number of termites in serum or glass vials and incubating in the dark at a fixed temperature (generally between 25 to 30°C) for a fixed time period (generally ranging from 1 to 3 hours) (see the scheme presented in Bignell et al., 1997). The CH4 produced during the incubation was then measured using a gas chromatograph for all studies. Although incubation conditions, including vial volume, incubation time, and incubation temperature, varied slightly across studies, the reported termite CH4 production rates were generally comparable across species. For studies that incubated termites with air and N2 (or H2) (e.g., Pester & Brune, 2007), we only included termite CH4 production rates measured from the incubation with air. For each eligible study, we extracted and tabulated termite CH4 production rates and other relevant variables (see the following section). We used μg CH4 g-1(termite) h-1 as the standardized unit, and if other units (e.g., μmol CH4 g-1(termite) h-1) were presented, we converted them into this standardized unit. In a few instances, we extracted data presented in figures using WebPlotDigitizer 4.5.

Note: On May 5, 2024, we made some corrections regarding the subfamily classification of termite species.

白蚁在热带及亚热带生态系统中可消耗大量植物生物质。在木质纤维素（lignocellulose）消化过程中，白蚁肠道内的共生产甲烷作用会产生强效温室气体甲烷（CH₄）。据估算，白蚁贡献了全球1%~5%的甲烷排放，该估算基于白蚁生物量与单位白蚁生物量的甲烷产率的乘积。然而，不同物种、属、科以及取食类群的白蚁甲烷产率存在显著差异，但目前学界对这种差异的认知仍较为匮乏。

本研究检索了1975年至2021年发表的文献，构建了一套统一标准化的物种级白蚁甲烷产率数据集。我们以关键词"termite AND methane"检索谷歌学术（Google Scholar），仅纳入采用培养法（incubation method）测定白蚁甲烷产率的研究。对每一篇符合纳入标准的研究，我们提取并整理了白蚁甲烷产率及其他相关变量（如取食类群）。我们采用μg CH₄ g⁻¹(白蚁) h⁻¹作为标准化单位，若研究中使用了其他单位，则将其转换为该标准单位。

本数据集共涵盖5科、65属的134个白蚁物种。白蚁甲烷产率区间为0至25.26 μg CH₄ g⁻¹(白蚁) h⁻¹，平均产率为3.74（标准差=4.08，样本量n=251）。已报道的甲烷产率主要集中在白蚁科（Termitidae）中。在不同取食类群间，土壤食性白蚁的甲烷产率普遍高于木食性白蚁。不过，已发表的数据仅占已描述白蚁物种的不足5%，因此我们希望本研究能够推动学界共同填补数据空白，加深对白蚁在关键生物地球化学循环及其他生态系统过程中作用的认知。

研究方法
我们从文献中收集白蚁甲烷产率数据，包括同行评议期刊论文与图书章节。数据收集工作于2020年10月启动，并于2022年2月完成更新。我们以关键词"termite AND methane"检索谷歌学术（Google Scholar），共获得7699条检索结果，随后对其进行纳入筛选。仅纳入采用培养法（incubation method）测定白蚁甲烷产率的研究：该方法将已知数量的白蚁密封于血清瓶或玻璃瓶中，在黑暗环境下以固定温度（通常为25~30℃）培养固定时长（通常为1~3小时）（详见Bignell等1997年提出的实验方案）。所有研究均通过气相色谱仪（gas chromatograph）测定培养过程中产生的甲烷。尽管不同研究的培养条件（如瓶体积、培养时长与培养温度）存在小幅差异，但已报道的白蚁甲烷产率在物种间仍具有可比性。对于同时采用空气与氮气（或氢气）培养白蚁的研究（如Pester & Brune, 2007），我们仅纳入空气培养组测得的甲烷产率数据。对每一篇符合纳入标准的研究，我们提取并整理了白蚁甲烷产率及其他相关变量（详见下文）。我们采用μg CH₄ g⁻¹(白蚁) h⁻¹作为标准化单位，若研究中使用了其他单位（如μmol CH₄ g⁻¹(白蚁) h⁻¹），则将其转换为该标准单位。在少数情况下，我们通过WebPlotDigitizer 4.5软件从图表中提取数据。

备注：2024年5月5日，我们对白蚁物种的亚科分类进行了部分修正。